The present invention relates generally to electronically controlled common rail fuel injection systems, and more particularly to the utilization of a rail pressure predictor model to improve accuracy of fuel injection in a common rail fuel injection system.
Common rail fuel injection systems come in many forms. For instance, a common rail fuel injection system might maintain fuel at injection pressure levels in the common rail, and then inject at that pressure by respective fuel injectors connected to the common rail. In another example, a separate actuation fluid, such as lubricating oil, is maintained in a common rail at a medium pressure level. This actuating fluid is then supplied to individual injectors which utilize the actuation fluid to hydraulically pressurize fuel within the individual injectors to injection pressure levels. In still another example, fuel is maintained in a common rail at a medium pressure level. The individual fuel injectors connected to such a rail have the ability to inject directly at the medium pressure level, or utilize the medium pressure fuel to hydraulically intensify the pressure of the fuel to be injected from the fuel injector. In all of these cases, the fuel injection rate is strongly a function of the rail pressure. Thus, as one would expect, the determination of injection control signals are currently based at least in part upon an estimated rail pressure. Thus, the accuracy of any given fuel injection event is strongly related to the accuracy of a rail pressure estimate used in determining the injection control signals that will be used in an attempt to deliver those desired injection characteristics.
Engineers have observed that rail pressure can vary substantially between injection sequences but also within an injection sequence itself. In many cases, these fluctuations in rail pressure can exceed 15% of the average rail pressure especially, and possibly to a larger extent, during cold starting. These fluctuations in rail pressure can be attributable to a number of phenomena. For instance, localized rail pressure fluctuations can be attributable to pressure waves bouncing around in the common rail due to such events as the opening and closing of various valves. More significantly, however, is the fact that in most cases the common rail is steadily supplied with fluid from a high pressure pump, but fluid is consumed from the rail by the injectors in brief gulps. Thus, one could expect rail pressure to drop with each injection event, and then recover between events. In an injection sequence that includes more than one injection event (e.g., pilot and main) it is probable that each injection event in the sequence could start at a different rail pressure. Thus, much more accurate delivery timings and quantities can be achieved if the rail pressure is known at the start of each injection event. Unfortunately, it is currently difficult to instantaneously obtain an accurate rail pressure measurement, and in the same instant, generate control signals based upon that rail pressure measurement, and again in that same instant carry out the determined control signal. Thus, one problem associated with improving delivery and timing accuracy of fuel injection events is the problem of accurately determining what the rail pressure will be at the beginning of each one of those events.
The present invention is directed to these and other problems associated with controlling common rail fuel injection systems.
In one aspect, a method of improving accuracy of fuel injection includes an initial step of determining injection characteristics for an injection sequence that includes at least one injection event and measuring the rail pressure prior to a start of the injection sequence. The rail pressure at a timing associated with each injection event of the injection sequence is estimated based at least in part on a rail pressure predictor model that includes the measured rail pressure. Control signal characteristics for the injection sequence are determined based at least in part on the estimated rail pressure and the injection characteristics.
In another aspect, a common rail fuel injection system includes a common rail with an inlet connected to a supply pump and at least one outlet connected to a plurality of fuel injectors. An electronic control module is operably coupled to the plurality of fuel injectors and includes a rail pressure predictor model.
In still another aspect, a rail pressure predictor model for predicting rail pressure in a common rail fuel injection system is recorded on a computer readable storage medium. In addition, an injector control signal determination algorithm for determining control signal characteristics based at least in part on a predicted rail pressure is also recorded on the computer readable data storage medium.